1. Field of the Invention
The present invention is generally related to an internal combustion engine with balance shafts and, more particularly, to a four cylinder four cycle in-line engine with a supercharging device in which two rotors of the supercharging device are provided with counterweights to balance the effect of secondary forces experienced by the engine.
2. Description of the Prior Art
Those skilled in the art of internal combustion engine design are familiar with many different types of balance shaft configurations used in internal combustion engines. Those skilled in the art of engine design are familiar with many different types of supercharging devices that utilize rotors. A Roots blower is one of several types of supercharging devices that employ two rotors.
U.S. Pat. No. 6,205,970, which issued to Iwata et al on Mar. 27, 2001, describes an engine balance shaft supporting structure. A casing accommodating therein a pair of balance shafts below the cylinder block comprises an upper casing and a lower casing that can vertically be split, and an oil pump body molded integrally with one of the upper and lower casings. In addition, one end of each of the two casings is inserted into the oil pump body for support therein and the two balance shafts are each supported on a bearing provided between the two casings in such a manner as to be split into two halves at the intermediate portion of the other end thereof.
U.S. Pat. No. 4,028,963, which issued to Nakamura et al on Jun. 14, 1977, describes an engine balancer. Balancer shafts are provided on the right and left of the crankshaft of an engine and so as to be driven thereby. Each balancer shaft has a balance weight divided into two portions, one on either side of a bearing supporting the balancer shaft. This construction protects the bearings from undesirable wear.
U.S. Pat. No. 6,189,499, which issued to Iwata et al on Feb. 20, 2001, describes a balancing device for a reciprocating engine. The balancing device for a reciprocating engine is provided which is improved so as not to disturb the compactification of an engine. There is provided a balancing device for a reciprocating engine comprising two balance shafts, gear connected to each other, a chain/sprocket mechanism for coupling at least one of the balance shafts with a crankshaft in an interlocking fashion, a chain tensioner for automatically adjusting the tension of the chain and a pump receiving portion integrally provided in a balance shaft holder for supporting the balance shafts for receiving a rotor of a lubricating oil pump, the balancing device being characterized in that the rotor of the lubricating oil pump is directly connected to the other balance shaft, and that the chain tensioner is disposed on a shaft end side of the other balance shaft.
U.S. Pat. No. 4,703,725, which issued to Weertman on Nov. 3, 1987, describes the mounting of an engine balancing device. An engine balance device utilizing rotating balance shafts is mounted in a housing means beneath the crankshaft and attached to the engine block by a plurality of legs spaced in the direction of the crankshaft axis to engage bearing journals located between cylinder bores. An oil pumping means evacuates oil from the housing means in cooperation with vacuum formation preventing air bleed means to the housing interior.
U.S. Pat. No. 4,819,505, which issued to Takubo et al on Apr. 11, 1989, describes balancer shafts for use in multicylinder engines. A balancer shaft for use in a multicylinder engine comprises a balance weight part formed to be eccentric in relation to a rotation axis of the balancer shaft and disposed along the alignment of cylinders in a cylinder block, an elongated shaft part extending from the balance weight part along the alignment of cylinders, a driving device provided on an end portion of the elongated shaft part for transmitting the rotation of a crankshaft in the cylinder block to the balancer shaft, a first journal provided on the end portion of the elongated shaft part, a second journal provided on a central portion of the balance weight part, and a third journal provided on an end portion of the balance weight part. The journals are supported by bearing portions provided in the cylinder block.
U.S. Pat. No. 5,253,547, which issued to Yoneyama et al on Oct. 19, 1993, describes a balancer device for an in-line engine. A balancer device is installed to an in-line engine comprising a balance shaft which includes first and second journals at which the balance shaft is supported through first and second bearings. The first bearing is disposed near the front part of the engine and set in a retainer for rotatably fixing the balance shaft. The second bearing is disposed near a generally center portion in the axial direction of the crankshaft and secured to a cylinder block. A pair of unbalanced portions are disposed near the second journal. The diameter of the first journal is formed smaller than that of the second journal to suppress the friction loss of the first journal.
U.S. Pat. No. 5,850,764, which issued to Bostelmann et al on Dec. 22, 1998, describes a crankshaft drive for an internal combustion engine. The crankshaft rotates at a predetermined direction and at a predetermined speed and a balance shaft extends parallel to the crankshaft and rotates at the predetermined speed of the crankshaft in a direction opposite to the predetermined rotating direction of the crankshaft. The crankshaft and the balance shaft carry balance weight means for balancing a mass of first order. An auxiliary shaft extends parallel to the crankshaft and rotates at the predetermined speed of the crankshaft in the predetermined rotating direction of the crankshaft. The auxiliary shaft carries a counterweight for balancing a residual moment resulting from the rotating balance shaft with respect to the rotating crankshaft.
U.S. Pat. No. 5,065,644, which issued to Shimada on Nov. 19, 1991, describes a counterbalance mechanism for an internal combustion engine. The engine has a crankshaft, a clutch, and a transmission including a main shaft rotatable by the crankshaft through the clutch and a countershaft rotatable by the main shaft through gears. A counterbalance mechanism includes at least a primary counterweight rotatable in synchronism with the crankshaft and a hollow shaft rotatably supported concentrically on the main shaft. The primary counterweight is integrally mounted on the hollow shaft. The clutch is corotatably mounted on the hollow shaft and operatively coupled to the crankshaft at the same speed as and in the opposite direction to the crankshaft.
U.S. Pat. No. 5,960,761, which issued to Kawakubo et al on Oct. 5, 1999, describes an engine with a balancer device for a vehicle. In order to suitably keep the weight balance of an engine while reducing a radial dimension of an engine, the crankshaft and a transmission shaft are supported in casings and are disposed to be substantially parallel to each other. A rear balancer and a front balancer are disposed with the crankshaft placed therebetween. An AC generator is disposed at an end portion of the crankshaft on the left side with respect to a plane passing through a center of gravity of an engine and being perpendicular to the crankshaft. A clutch is disposed at an end portion of the transmission shaft on the right side with respect to the plane. The clutch is separated from the plane at a distance smaller than that between the AC generator and the plane, so that the weight balance of the engine is suitably maintained by disposing the rear balancer and the front balancer on the clutch side.
U.S. Pat. No. 4,813,857, which issued to Kawakami on Mar. 21, 1989, describes a Roots blower. In a Roots blower having a casing, two rotors rotatably housed within the casing, and at least two grease-enclosing bearing units to rotatably support the rotors, the invention is characterized by a bypass groove which is formed for each of the bearing units so as to communicate between a first chamber defined by the casing and the rotors on the side of one axial end of the bearing unit and a second chamber formed by the casing in the bearing unit on the other axial end of the bearing unit, and in that a pair of pressure loaded seal rings is disposed on axially opposite sides of the bearing unit in such a way that one periphery of each seal ring is secured to a stationary portion of the bearing unit and the other periphery thereof is free to move selectively into or out of contact with a movable portion of the bearing unit according to the presence or absence of a pressure difference produced by a delay in a pressure-balancing action of the bypass groove between the two chambers so that the seal ring prevents bearing grease from leaking.
U.S. Pat. No. 4,215,977, which issued to Weatherston on Aug. 5, 1980, describes a pulse-free blower. A three lobe Root""s blower is provided with feed back structure to bring the gas trapped in the impeller well volumes up to the discharge pressure prior to delivery. An essentially uniform and pulse-free discharge is produced by having a constant feed back flow rate which is achieved by always having a trapped impeller well volume in communication with the outlet via feed back structure which is sized to yield a continuous fee back flow rate.
U.S. Pat. No. 4,666,385, which issued to Okamoto et al on May 19, 1987, describes a Roots type blower. The blower is disclosed having rotors with a twisted shape and projections on the pitch side. The blower is compact in the axial direction, because the projections work as gearing between the rotors. Therefore, it is not necessary to provide additional gears for driving the rotors.
U.S. Pat. No. 4,781,541, which issued to Sohler et al on Nov. 1, 1988, describes an external axial rotary piston blower with noise suppressing transfer ports. An external axial rotary piston blower for quarter-roller type of construction with transfer ports leading to the outlet in the casing runway surfacing or inner peripheral surface of the housing with length differing relative to each other and increasing cross section differing toward the outlet, the greatest length of which can be permitted to be dimensioned or measured only such that the transfer ports are first opened when the inlet is closed off by the piston traversing the same.
The patents described above are hereby expressly incorporated by reference in the description of the preferred embodiment.
Engine balance shafts are provided in certain types of engines in order to counterbalance the forces generated by the movement of the pistons and connecting rods within the engine in coordination with the rotation of a crankshaft supported by bearings disposed within the engine structure. Certain types of internal combustion engines, such as four cylinder in-line engines, can be essentially balanced without the use of additional counterbalance shafts to the extent that all primary vertical and horizontal inertia forces and moments are cancelled out as well as secondary moments. However, certain secondary forces perpendicular to the crankshaft axis are not inherently balanced and therefore remain unresolved during the operation of the engine. These unresolved forces create undesirable effects with regard to the noise, vibration, and harshness of the engine""s operation. These forces require some type of compensation, particularly in engines having displacements greater than 2.0 liters. Primary forces are inertia forces created by the acceleration of the piston assembly mass caused by the rotating crank pin""s projected motion along a line of stroke due to the reciprocating motion of the piston assembly. Secondary forces are those inertia forces caused by the projected motion perpendicular to the line of stroke caused by the rotating motion of the connecting rod. In other words, the secondary force is due to the addition or subtraction in piston acceleration produced by the rotating crank pin increasing or decreasing the inclination of the connecting rod to the line of stroke. During the initial 90 degrees of crankshaft rotation, this secondary movement of the connecting rod is away from the line of stroke, thus adding to the piston movement while during the second 90 degrees of crankshaft rotation, this secondary movement of the connecting rod is toward the line of stroke. This subtracts from the distance the piston moves. Furthermore, secondary forces increase and decrease their magnitude at twice the frequency of the primary force. A detailed description of the cyclic forces relating to internal combustion engines is available in xe2x80x9cAdvanced Engine Design QandAxe2x80x9d by Thrasher Engineered Performance. Another explanation of engine cyclic engine forces is provided in xe2x80x9cReciprocating Balancingxe2x80x9d by Professor B. J. Stone. Both of these articles were obtained from associated internet sites.
Four cylinder four cycle in-line engines have this unbalanced secondary force which becomes objectionable when the displacement of the engine exceeds approximately 2.3 liters. Common practice in the prior art is to install twin counterrotating balance shafts which rotate in opposite directions at twice the crankshaft speed. These counterrotating balance shafts are positioned to cancel the secondary forces. It would therefore be significantly advantageous if a device could be provided which counterbalances the secondary force of the four cylinder four cycle in-line engine without requiring additional balance shafts to be provided which serve no other purpose except to perform this balance function.
An engine, made in accordance with the present invention, comprises a crankshaft supported for rotation about a vertical axis and a plurality of pistons connected to the crankshaft in which each of the plurality of pistons is disposed for reciprocating movement within an associated one of a plurality of cylinders of the engine. In addition, first and second shafts are provided. Each shaft is supported for rotation about an individual axis of rotation at a rotational velocity and in a rotational direction. Each of the first and second shafts has a center of gravity which is radially displaced from the axis of rotation by a preselected amount. The first and second axes of rotation are generally parallel to the vertical axis about which the crankshaft rotates. The first and second rotational directions are opposite to each other and the first and second rotational velocities are each generally equal to a preselected multiple, such as two, of the rotational velocity of the crankshaft.
In a preferred embodiment of the present invention, it further comprises a housing in which the first and second shafts are supported by the housing for rotation within the housing. The housing is rigidly attached to the engine.
In a particularly preferred embodiment of the present invention, the first and second shafts are first and second rotors of a supercharging device. The supercharging device is preferably a Roots blower. In a preferred arrangement, a first plane, bisecting each of the plurality of pistons and containing the vertical axis of the crankshaft, extends between and is equidistant from the first and second axes of rotation of the first and second shafts.
The primary advantage of the present invention is that it allows an engine to be completely balanced through the use of the rotors of the supercharger which is used for the independent purpose of providing additional air to the engine. In other words, through the use of the present invention, a supercharged engine can be satisfactorily balanced without requiring additional balance shafts beyond those two rotors used in the supercharger.
In a particularly preferred embodiment of the present invention, the engine is a powerhead of an outboard motor. The engine can further comprise first and second pairs of counterweights attached to the first and second shafts to cause the first and second centers of gravity to be radially displaced from the first and second axes of rotation by the first and second preselected amounts. The first and second pairs of counterweights can be formed as integral parts of the first and second shafts or, alternatively, can be individual components that are attached to the first and second shafts. Although a preferred embodiment of the present invention incorporates a pair of counterweights on each of the first and second shafts in order to balance the secondary forces without inducing additional unbalanced moments, it should be understood that this arrangement is not required on all embodiments. The shafts themselves can be shaped to result in the desired imbalance.
The preselected multiple which describes the relationship between the rotational speeds of the crankshaft and of the first and second shafts is equal to two in a preferred embodiment of the present invention. In other words, the first and second shafts counter rotate at twice the speed of the crankshaft.
The plurality of pistons in a preferred embodiment of the present invention comprises four pistons connected to the crankshaft and dispose in four cylinders. The four cylinders are disposed in an in-line configuration and the engine is a four cycle engine in a preferred embodiment. In a preferred embodiment of the present invention, the crank pins of the crankshaft are all arranged in a common plane. This arrangement is referred to as a planar crankshaft and is illustrated in FIG. 3.
The first and second shafts are connected in torque transmitting association with the planar crankshaft. The first shaft can be connected directly in torque transmitting association with the planar crankshaft and the second shaft can be connected in torque transmitting association with the first shaft. In other words, within the housing, the first and second shafts can be geared together and either one of the two shafts can be driven by the crankshaft by a timed arrangement to the crankshaft positions, either by a chain connection, a flexible cogged belt connection, or through a pair of gears.